1. Technical Field
This invention relates to metalworking and more particularly to an improved punch head for a sheet metal punch press.
2. Background Art
Slider crank punch heads have for many years been used on punching machines. U.S. Pat. No. 4,272,812 illustrates a punching machine using a slider crank mechanism which operates a punching tool.
A punch press is normally associated with a two axis sheet positioning mechanism, for relative positioning of a work sheet at an appropriate position beneath the punch head. The punch head, mounted above the punching area, is connected through a suitable interposer to operate a punch in conjunction with a die, located beneath a work sheet support table. The punching head operates a punch which is contained in an upper tool holder and is aligned with an appropriate die, contained in a lower tool holder, for punching a selected hole in the workpiece.
Typical prior art punch presses have normally been designed with sheet positioning function and the punching function placed in series. During sheet positioning a two axis, X-Y, table positioning mechanism brings a sheet into a correct position to be punched. When the sheet is stopped and in the correct position to be punched the punching function commences. When punching, the punch head motion is supplied by a crank shaft starting at top dead center and making a single revolution to punch a hole in the worksheet and repark back at top dead center. From a timing standpoint, the stroke of the punch head crankshaft is usually designed to simply be adequate to take the punch from a safe position in the upper toolholder down through the sheetmetal workpiece and back to a safe position retracted into the upper tool holder. Normally no more stroke than is necessary to move the punch through the punching zone of the material is provided. In the past the higher punching rates have normally been achieved by increasing the crankshaft speed to minimize the amount of time it takes for the crankshaft to move through the 360 degree motion associated with punching a hole.
Typically, the crankshaft rpm is far in excess of the number of hits per minute the press is rated for when cycling in an intermittent mode of a single revolution of the crankshaft by application of a clutch and brake cycle for each hole that is punched. Once the clutch is engaged almost the entire 360 degrees motion of the crankshaft results in the punch being exposed below the upper tool support into the punching zone and does not allow the table to be moved during the interval.